The present invention was made as a further development of the valve shown and described in the copending U.S. Patent application of McGee, Ser. No. 800,437, filed May 25, 1977 (now U.S. Pat. No. 4,138,091) for a drive nut and torque plate assembly for the valve, the copending U.S. Patent application of McGee, et al, Ser. No. 800,438, filed May 25, 1977 (now U.S. Pat. No. 4,149,558) for a selective back seat for the valve.
The foregoing, in turn, represent developments of valves described in the following prior U.S. patents.
______________________________________ Patentee U.S. Pat. No. Issue Date ______________________________________ Crain, et al 3,349,789 Oct. 31, 1967 McGee 3,789,875 Feb. 5, 1974 Boitnott 3,990,679 Nov. 9, 1976 ______________________________________
Others have worked with fusible materials in order to provide safety devices for valves. Examples are shown in the following prior U.S. patents:
______________________________________ Patentee U.S. Pat. No. Issue Date ______________________________________ Wicke 3,771,540 Nov. 13, 1973 Allen 3,788,600 Jan. 29, 1974 Wicke 3,842,854 Oct. 22, 1974 Wicke 3,896,835 Jul. 29, 1975 ______________________________________